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Police Sirens – Mechanical vs Electronic

Everyone is familiar with police sirens but may not know there are many kinds on the market. The two primary types of sirens used by law enforcement are pneumatic and electronic devices. Here we will go over what makes each siren type unique.


Before Traditional Sirens Were Created

Before either type of siren was made, first responders depended on steam whistles or church bells. Eventually, first responders began using fire horns. While each early siren was effective for a short time, changes had to be made to keep up with population and traffic. As areas became more congested, the siren had to change to be able to be effective. Throughout time, there have been many audible warning devices used by first responders but only two have stood the test of time.



Pneumatic Police Sirens



Pneumatic devices are referred to as mechanical or coaster sirens. Pneumatics are different than an electronic siren because it is driven by an electronic motor. In a pneumatic siren, there is a free aerophone that contains a rotating disk with holes. The holes interrupt air flox from fixed holes on the outside of the unit and prevent or allow air flow at certain intervals.

The main problem with this siren type is that it uses forced air. The accidental or sudden loss of air can cause the siren to lose sound without notice. Pneumatic sirens are often found on fire trucks. Some ambulances and rescue squads still use this device because it can create urgent high sound pressure decibels (123 dB at 10 feet).


Electronic Police Sirens


Electronic sirens for police were created in 1965 by Ronald H. Chapman and Charles W. Stephens. These inventors wanted to copy the sounds of a pneumatic siren in a more reliable device. While electronic versions sound like pneumatic sirens, they are built differently and don’t rely on forced air.

Electronic sirens use oscillators, modulators, and amplifiers to create sound. Together, these components make siren tones such as wail, yelp, phaser, hi-lo, piece, priority, manual, airhorn, scan, and more. Sound is delivered through external speakers. Many patrol cars have electronic audible units.


Further Reading

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